The present invention relates to a closure for a closure-container combination having a peelable seal and that is sterilized using a retort process. The closure causes the seal to maintain a positive pressure against a container lip as the container undergoes sterilization by retort processing thereby minimizing the risk of leakage under the seal.
In recent years, packaged products which are room temperature storage stable yet ready-to-use upon opening, i.e. they require no cooking or heating before use, have become extremely popular with the consumer. For many food products, this trend requires only minor packaging changes, such as modifying the package size to be consistent with the anticipated consumer use pattern. However, for products prone to bacterial contamination and spoilage, such as milk-based beverages, soups, and many other low acid food products, this trend presents some major packaging challenges.
For example, milk-based and low acid food products need to be sterilized to reduce the initial viable bacterial concentration in a product, thereby reducing the rate at which the product will spoil and lengthening the product's shelf-life. One procedure for reducing the viable bacterial concentration is sterilization by retort processing. In the retort process, a chilled or ambient temperature product is poured into a container and the container is sealed. The container may be sealed by melding two sections of the container material together, such as by heat-sealing a seam on a pouch, or the container may be sealed by bonding a seal to the lip of the container, such as by induction sealing a foil-lined seal to a barrier polymer material bottle neck. The filled package is then sterilized at high temperature in a high pressure water bath. In a typical commercial production rate retort process, the package is heated from an ambient temperature of about 75° F. to a sterilizing temperature in the range of from about 212° F. to about 270° F. As the exterior surface of the package is heated, the package contents are heated and the internal (vapor) pressure increases. By concurrently, submerging the package in the water bath, a counteracting external pressure increase is applied to the container. Although the retort process is an efficient sterilization process, it is harsh on packaging materials because of the temperature and pressure variations involved. Materials commonly used for stand-up, reclosable containers, such as plastic bottles, tend to soften and distort during retort processing. Materials used for seals can soften and, because the seal material is distinct from the container material, can form small gaps or pinholes at the bond interface. These gaps or pinholes can allow product to vent out of the container as the internal pressure increases during the retort process and can allow process bath water to enter the container as the internal pressure decreases relative to the external pressure and the package returns to ambient conditions. Because the packaged beverage and the process water may pass through very small gaps at the bond interface, this event may occur even though the product appears to have an acceptable seal. Moreover, the container and seal may enter the retort process in a less than ideal condition because the process to adhere the seal to the container can cause the neck, the lip, the threads or a combination thereof on the container to distort slightly. If the seal is transferred to the neck with a closure mounted on the container, the skirt, top, threads or a combination thereof on the closure may distort during the seal transfer process. These material failures can increase the number of manufacturing errors and can allow for product contamination even on packages that appear to meet quality standards.
Barrier pouches minimize the risk of material failures during retort processing because the pouch usually has sufficient flexibility that it can alter its shape in response to the over-pressure conditions of the retort process. Moreover, barrier pouches generally have minimal headspace within the sealed pouch so the packages are less affected by the external pressure changes than are packages with relative large headspaces, such as semi-rigid bottle-like containers. Further, the seals or bonds are created by melding the pouch material to itself thereby creating strong, non-distinct bonds. Hence, well-sealed packages which are not dependent on maintaining their original shape can be produced. However, the pouches usually require specialized devices, such as sharp-tipped straws, to open the package and do not allow the consumer to reclose the package after opening.
For bottles or similar stand-up containers that are sealed such that the seal can withstand the retort process, a different problem may be created. The seal may adhere so tightly to the container lip that when the consumer attempts to remove the seal, the seal may be very difficult to remove from the container, and/or may tear into small pieces and leave fragments along the container rim. If the product is a beverage or similar liquid product, the product may settle under the seal fragments as the beverage is dispensed. This can make the product aesthetically unacceptable and unpleasant for repeated use by the consumer and increase the probability of bacterial contamination under the seal fragments. Further, the user risks being cut or scratched by the remaining foil bits along the container lip. Semi-rigid containers also have relatively large headspaces thereby allowing the user to shake and remix the product immediately before dispensing. However, during retort processing, the air-filled headspace will be affected more rapidly than the liquid product by the temperature changes increasing the pressure against the seal and thereby increasing the probability of seal failure.